Survey of Meloidogyne incognita and Thielaviopsis basicola: Their Impact on Cotton Fruiting and Producers' Management Choices in Infested Fields

Abstract

A survey of 100 cotton fields selected randomly in 1995 and 1996 was conducted in the High Plains of Texas to determine the incidence and potential severity of Meloidogyne incognita and Thielaviopsis basicola. Information was obtained from producers for each field on their nematicide application rates and fungicide seed treatments. The percent of squares and bolls set was evaluated for 20 plants in each field during late July 1995 and early August 1996. Thielaviopsis basicola was identified in 55% of the fields in 1995 and 73% of the irrigated fields in 1996. Meloidogyne incognita was found in 39% and 43% of the fields in 1995 and 1996, respectively. Both M. incognita and T. basicola were found together in approximately 30% of the fields. The average rate of aldicarb used in 1995 and 1996 was higher when fields were infested with both T. basicola and M. incognita than for fields infested with none or only one of the pathogens. However, there was no relationship between the use of fungicide treatments active against T. basicola and the potential for root necrosis, or presence of either or both pathogens (T. basicola and M. incognita). Aldicarb rates and usage of fungicide seed treatments were chosen by producers before fields were surveyed (i.e., the survey did not influence grower practices). In 1995, but not in 1996, the association of M. incognita and potential root necrosis (based on a bioassay from soil samples) was negatively correlated with the number of squares, percentage of squares set, and percentage of bolls set. The association between M. incognita and T. basicola, or potential severity of root necrosis, could not be correlated with fruit attributes in 1996 under warm spring conditions but was negatively correlated with fruit attributes in 1995 under cool spring conditions.